Between 12 and 13 December 2015, the Nigerian military conducted a crackdown of the Islamic Movement of Nigeria (IMN), a pro-Iranian Shia group based in the northern city of Zaria. The military action led to hundreds of IMN members reportedly being killed and the group's leader, Sheikh Ibrahim Zakzaky, taken into custody. As the movement's followers continue to call for his release, the incident echoes the first rumblings of the Boko Haram insurgency, which has claimed more than 17,000 lives, according to Amnesty International, and displaced some 2.5 million people since 2010. The incident also risks opening a new front of geopolitical struggle between Shia Iran and Sunni Saudi Arabia, with the potential of stoking sectarian divisions in Africa's largest economy.

The IMN's rhetoric points to the aspiration of establishing an Islamic state through an Iranian-style revolution, a central theme of Zakzaky's sermons over the years. This has put the group at loggerheads with the country's secular authorities since the early 1980s, and led to occasional violent confrontations. In 1982, for instance, Zakzaky was arrested on a preaching tour in the northern city of Sokoto for calling for a revolution. The government sees the group as a national security threat; 62-year-old Zakzaky has been periodically incarcerated for alleged incitement to violent Islamic revolution and subversion.

Zakzaky was emboldened by the 1979 Iranian revolution.

The IMN started in 1978 at Ahmadu Bello University Zaria as a Muslim student movement led by Zakzaky, who was inspired by the Egyptian Muslim Brotherhood. Like the better-known Nigerian militant group Boko Haram, IMN openly denounces the Nigerian state as un-Islamic and proclaims its goal as establishing an Islamic state. The IMN claims to have between seven and 10 million members, though there is no concrete proof of this figure. According to one former member, the true figure is likely closer to six million. The group condemns democracy and discourages involvement in democratic elections; holds traditional and constitutional leaders in contempt; and violates state laws, including traffic regulations.

Zakzaky was emboldened by the 1979 Iranian revolution. He established close relations with the Islamic Republic in his student days. His alliance with Iran created a rift with vocal and influential Saudi-funded Salafi clerics in Nigeria at the time.

He remained a Sunni until 1996 when he and many of his followers converted to Shia Islam. However, his conversion seems to have been more political than theological. On a number of occasions Zakzaky has declared the IMN to be a nonsectarian organisation, and he has repeatedly downplayed the Shia links of the organisation, attempting to appeal to a broader Muslim audience. In 2014 Zakzaky told the incumbent head of Nigeria's Human Rights Commission that the IMN was not a Shia sect.

Zakzaky's conversion raised concern among Nigeria's Shia minority, whose members are generally well integrated in society and object to Zakzaky's confrontation with the state in the name of their faith. They accuse Zakzaky of forming a personality cult around himself, introducing innovations in Shia Islam, and flouting religious fatwas. His disobedience to the state makes them nervous that Zakzaky is giving Shia Islam a bad name, and they note that despite his leadership of a large Shia movement, Zakzaky has no Shia theological training.

A State Within a State

Like many influential religious Nigerian organisations, IMN operates like a state within a state. It has its own leadership structure across Nigeria with Zakzaky at the helm. Followers receive orders from him through his lieutenants spread across the country. The state has felt threatened by Zakzaky's strong and elaborate network, and its refusal to recognise the Nigerian state.

The face-off between the IMN and the military has boiled over in the past, notably in July 2014 when a clash left 34 members, including three of Zakzaky's sons, dead.

The latest incident began on 12 and 13 December 2015, when soldiers opened fire on IMN followers, killing at least 300, according to Human Rights Watch. The army has not given a casualty figure, but denies the HRW reports. IMN members had blocked a major road outside the group's Husseiniyya religious center, where hundreds had gathered for a religious ceremony, obstructing traffic. The convoy of Nigerian Chief of Army Staff Yusuf Buratai was caught up in the logjam. The army accused the Shias of trying to assassinate the army chief and soldiers opened fire. The Movement denies the charge and accuses the military of a premeditated attack.

The genesis of the Boko Haram insurgency looms large.

Zakzaky was seriously injured and taken into military custody where he remains, while his home and several IMN religious centers were destroyed. Scores of his followers were arrested. The dead included Zakzaky's deputy, an IMN spokesman, and its head of security. Several reports claim between one and three of his sons were killed. According to another IMN spokesman, Zazaky lost a total of six children in the 2014 and 2015 clashes, with only one of his sons and two daughters surviving.

The genesis of the Boko Haram insurgency looms large over this incident as it was set off by a similar series of events. Boko Haram started as a radical Salafi group with the mission of enthroning an Islamic state in place of Nigeria's secular government. This is also the aim of the Shia IMN. Boko Haram's insurgency started in 2009, following a clash between armed policemen and a funeral procession of the group, which left several of its members injured. They launched reprisals, leading to a six-day military intervention that left at least 800 dead. When Boko Haram leader Mohammed Yusuf was killed in police custody shortly after being arrested by soldiers, it caused the group's surviving members to go underground for a year and was a foundational grievance when they reemerged in 2010 under the leadership of Yusuf's deputy Abubakar Shekau. The same scenario could play out if Zakzaky dies in custody.

The crackdown has worsened Sunni-Shia tensions.

To avert another Islamist insurgency erupting, on 15 December the National Supreme Council for Islamic Affairs (NSCIA), the highest Islamic decision-making body in Nigeria, formed a 10-man committee to intervene between the Nigerian authorities and the IMN to reach a settlement. Such interventions could have a positive impact, giving IMN members a sense of belonging. However, the IMN has set the release of Zakzaky as a precondition for negotiations.

But even if the NSCIA succeeds in brokering a truce between the IMN and the Nigerian government, the Zaria crackdown has worsened tensions between Sunni and Shia communities. Since the crackdown, some Saudi-sponsored Salafi clerics have been expressing their support for the Nigerian military chief's response to the IMN, and mounting sustained vitriolic attacks on Shia. One video clip shared in northern Nigeria shows the National Chairman of Jama'atul Izalatil Bid'ah Wa'iqamatus Sunnah (JIBWIS), a prominent conservative Islamic organisation, Sheikh Abdullahi Bala Lau, saying "The Sunnis should rise up, as the emir of Kano said, this country is not a place where the companions of the Prophet would be insulted without generating any response."

Such attacks have drowned the voices of more moderate Sunnis who call for understanding and sympathy with the IMN to avoid creating another insurgency similar to Boko Haram. On 14 December the Sultan of Sokoto, Muhammad Saad Abubakar, the highest spiritual figure among Nigerian Muslims, issued a statement via the NSCIA, which he chairs, saying: "While there are claims and counter-claims on what actually precipitated the latest heart-rending incident,‎ the NSCIA‎ urges the authorities to exercise restraint. The history of the circumstances that engendered the outbreak of militant insurgency in the past, with cataclysmic consequences that Nigeria is yet to recover from, should not be allowed to repeat itself."